A variety of fluids, such as lubricants and chemical reactants, are used in modern industry. For example, compressors and other machines reduce internal friction between parts by injecting a lubricant, such as oil or grease, into critical bearing surfaces and reciprocating part junctions. If the flow of lubricant is interrupted, compressors and other industrial tools can be seriously damaged or destroyed. On the other hand, too much lubricant can unnecessarily increase the operating expenses of the machinery and can contaminate the environment. Poorly controlled fluid flow can affect the result in other industrial operations, such as well bore components, gas pipeline components, and oil and gas production.
A variety of systems are used to distribute lubrication in industrial machine applications. Originally, multiple pumps were used to supply oil to multiple points. It was found that, in such systems, the flow was not sufficiently uniform between lubrication points, with some points being starved for lubricant while other points wasted lubricant with excessive flow.
A more reliable system uses a pump to pressurize a fluid distribution line and a positive displacement divider block, also referred to as a divider valve, to distribute a lubricant, such as oil, from the single pump outlet line to multiple injection points. A typical divider block is operated by the pressure of the incoming fluid to divide the fluid into multiple output channels. Divider blocks typically include multiple internal pistons that are activated by the flow of the incoming oil. As the oil moves the pistons, internal hydraulic circuits open and close to distribute a known volume of lubricant to each of the multiple outputs for each cycle of the pistons. Because the internal hydraulic circuits are progressively opened and closed by the flow of the incoming oil, no external power source is required to operate the divider block, and no external timing signal is required to deliver a prescribed amount of oil to each outlet line. The bore and stroke of each piston determines the amount of fluid delivered with each cycle of the divider block. Because these dimension are known, the amount of oil distributed for each cycle of the divider block can be readily calculated, and if the number of cycles in a unit of time is tracked, the flow rate can be readily determined. The simplicity and reliability of divider blocks have lead to their wide acceptance in many applications.
Divider blocks can still fail to provide adequate lubrication in some circumstances. For example, a pump failure can reduce the inlet flow to the divider block, reducing the amount of lubricant distributed. The divider block can become clogged, jammed, or sufficiently worn so as to reduce fluid or lubrication flow to specific points.
U.S. Pat. No. 5,835,372 to Roys et al. for an “Integrated Fluid Flow Evaluation Apparatus and Method,” which is hereby incorporated by reference, describes a system for monitoring the cycles of the outputs of a divider block. In accordance with the Roys et al. patent, a fluid flow sensor can be mounted at an outlet position of a divider block to detect cycles of the combined outlets. The sensor includes a magnet, typically mounted on a rod coupled mechanically or magnetically to the piston. The magnet moves back and forth as the piston moves. A reed switch positioned along the path of the magnet is operated as the magnet passes, so each signal from the reed switch corresponds to a cycle of that dispensing valve piston. Knowing the bore and stroke of the piston, the system can determine the lubricant flow rate, e.g., the number of pints per day, at an outlet by counting how many times the reed switch closes during a measured time period. For example, if the piston expels 10 cc of lubricant with each cycle and the reed switch closes three times each minute, a lubricant flow of 30 cc/min should pass through that outlet of the divider block. Since all pistons of a divider block go through one complete dispense process during each period that the valve cycles, a user typically connects a single sensor to one outlet of the divider block to count valve cycles, and then infers the fluid flow from all the outlets.
A fluid flow monitor associated with the sensor includes a microprocessor that counts reed switch activations and a display mounted on the monitor to provide control information to field personnel. The monitor can also send a signal to shut down the lubricated equipment if the flow of lubricant is below a minimum level. Although stored data is primarily viewed in the field by maintenance personnel, the monitor can be connected to a central control panel.
While the system of Roys et al. displays some control information at each divider block, a field service technician is typically required to read the information from each monitor display to check the status and history of that individual block. Although a “hard-wired” control panel near the divider block can be used to collect data from multiple sensors, running wires adds to the cost of installation and may be difficult or impossible in some situations, such as in areas containing explosive gases or at long distances from the control panel. In many applications a field maintenance operator cannot electrically download information from a monitor on-site, because in an explosive hazard environment, it is forbidden to make or break electrical connections because of the possibility of causing a spark.
Also, although the Roys et al. system provided information about the fluid that exited the divider block, it provides no information about whether the fluid actually reached the injection point. Thus, leaks between the divider block and the injection point can go undetected.
Relatively small volume fluid flow is not typically measured in-line because of a lack of cost-effective measuring equipment. Turbine-type measurement devices are used in fluid systems having a high volume of fluid flow, for example, measured in gallons per minute or liters per minute. Turbine devices are not suitable for measuring low volume, that is, in the range of about ten gallons or less per day. Such low volumes are typically pumped by lubrication and chemical pumps. Positive displacement pump-type measuring systems typically use gears and are typically expensive and cannot accurately measure low volumes. Such devices are impractical to use in large numbers to monitor fluid flow at the large number of points necessary to characterize fluid flow in a large system and they are typically not sufficiently accurate at low volumes. Accurate measurement of the flow of relatively small amounts of fluid at the relatively high pressure used in some systems has been a problem in the industry.
In the oil and gas industry, the amount of fluid used in many circumstances is determined by observing a “draw down” gauge at a tank. Such gauges are not precise, and while such gauges indicate the amount of fluid that left the tank, they do not directly measure the fluid that was applied at the injection point. Leaks or wrongly set valves may prevent fluid that left the tank from arriving at its intended injection point. The lack of a practical method of monitoring the divider block for measurement, trending and control of fluid.
The accuracy of fluid flow measurement based on a cycle counter on a divider block can decrease over time. As the divider block wears over hundreds of thousands or millions of cycles, the amount of fluid delivered for each cycle of the piston can vary, with some of the fluid bypassing the piston and traveling to a point of least resistance. Then, some lubricant flows back around the piston instead of being forced into the outlet, and the flow calculations based on the piston size to each lubrication point or fluid injection point become inaccurate.
U.S. Pat. No. 6,212,958 to Conley describes the use of a blade that extends into the pipe and the degree of deflection of the blade as fluid flows is an indication of fluid flow. Extending a blade into the fluid can affect the fluid flow and the blade can deteriorate over time.
Another solution to measuring fluid flow has been to use a thermistor to infer fluid flow based upon a change in temperature. This method is only for monitoring movement of fluid and cannot monitor in quantity of fluid. Such units are expensive, are impractical to attach to a large number of fluid flow points to accurately monitor and characterize a large system and are not permitted in areas where explosive gases or vapors are present. There are sometimes disagreements between suppliers and users about the amount of fluid that has been delivered.
When fluid flow is monitored, using the devices described above, the information available has been limited primarily to current flow and has been used primary to shut down equipment or to sound an alarm. This information is typically inadequate for precise monitoring. For example, when a single compressor in a multiple compressor system fails, it would be difficult to detect that the failure was caused by an intermittent lubrication problem, particularly if the lubrication system was functioning adequately at the time of failure. Service personnel would likely observe that the other compressors are satisfactory and determine that the lubrication system is operating properly and assume that the fault was in the compressor itself. In fact, the lubrication system may be operating properly at the time the technician observes the system, but a previous undetected problem may have damaged the compressor to the point where it fails later, when it is receiving adequate lubrication. Thus, it has been very difficult to diagnose some lubrication problems and such problems cost industry a great deal in ruined equipment.